Abstract : Problems pertaining to spacecraft charging at near-geosynchronous orbit were investigated using data from P78-2 SCATHA collected in 1979-80. These studies included specification of significant aspects of the near-geosynchronous environment, effectiveness of active control systems and verification of computer modeling of satellite potentials. Environmental specification studies were made of major plasma sheet boundaries, near-geosynchronous particle fluxes and long term prediction of hazardous geomagnetic conditions. Work was begun on magnetospheric modeling. Unfortunately, the particle beam active control system caused the failure of two instruments. These events were thoroughtly studied but some uncertainty remains concerning the causes of the problems. Comparisons of spacecraft discharge techniques indicated the x sub e (+) plasma source was the preferred operational mode. Satisfactory agreement with observed charging levels was obtained when the NASCAP/AFGL computer model was used with environmental input derived from observed particle fluxes. A secondary research effort focused on studies of ionosphere-magnetosphere interactions in the polar cap and auroral zone. Air Force measurements of S3-2 electric and magnetic fields and electron and thermal plasma fluxes were used as well as DMSP auroral imagery.